I'd like to change things to split 6.3 into 6.3 to 6.9. However, this
means that the existing 6.4 to 6.7 will become 6.10 to 6.13. Will that
make the report too much harder to use? I don't know.

I think that would be an improvement. It's been years since I did any work with R5RS, so I'm not attached to any memory of its organisation. However, playing around with a personal implementation for the current draft, I have more than once been trying to find one of the data types and had to sort of zero in on it because it was in 6.3 ("it's not in the table of contents, so it must be an 'other'. Okay, off to hunt for the right subsection").